1. Field of the Invention
This invention relates to a zoom lens barrel having a focusing adjusting mechanism.
2. Related Background Art
In a zoom lens barrel capable of effecting AF (auto focusing), if a clutch or the like is provided to thereby provide one-operation zoom when the zooming operation is made into the direct advance type, the structure will become complicated and costs will become high and, therefore, a focusing operating ring is provided on a zoom operating ring so as to be movable in the direction of the optical axis with the zoom operating ring.
If such an arrangement is adopted, during AF, the focusing operating ring can be retained so that fingers may not touch it, and during MF (manual focusing), zooming is effected with the focusing operating ring retained so that fingers may touch it, whereby focusing can be done smoothly without changing the shift from zooming to focusing.
In the prior art described above, there is adopted the forward lens movement system in which a one-unit lens is moved back and forth in the direction of the optical path to thereby effect focusing, but the one-unit lens is relatively large in lens diameter as compared with the Other lens units, and this has led to a problem that when a motor is driven by AF, the load becomes great and the focusing speed becomes low.